Impedance measurements are frequently employed to determine the values of various parameters. In one specific application, the volume of dielectric liquid fuel in a tank is monitored by immersing electrodes in the liquid. The capacitance of the liquid between the electrode has been measured in many ways, e.g. by employing it as a frequency determining impedance of a variable frequency oscillator, the frequency of which is monitored in a conventional manner. In other systems, the capacitance is measured by applying a sinusoidal voltage to the electrodes and determining the voltage flowing to the electrodes. Since the amplitude of the current has a predetermined value the current provides a measure of the capacitor value.
In systems of this type, the dielectric liquid fuel is subject to contamination due to various factors, such as dirt and water. The contamination modifies the impedance between the electrodes so that an equivalent circuit of the impedance is a capacitance, determined by the dielectric fluid, shunted by a resistor having a value determined by the contaminants. Some of the prior art systems have been able to provide compensation for the variable resistance due to the contamination. However, there is, to my knowledge, no prior art system which has provided a measurement of the resistance due to the contamination.
It is, accordingly, an object of the present invention to provide a new and improved apparatus for measuring the value of a capacitor.
It is another object of the present invention to provide a new and improved apparatus for measuring the value of a capacitor and for measuring the value of a resistor in shunt with the capacitor.
A further object of the invention is to provide a new and improved system for monitoring the amount of liquid dielectric fuel in a tank.
A further object of the invention is to provide a new and improved system for monitoring the amount of liquid dielectric fuel in a tank and for providing a measurement of the resistance of contaminants in the liquid.